Some people think the differences between qualitative and quantitative research are worth arguing about. Others prefer to get mired in distinctions between critical and empirical research. I think it is best to make use of the diversity of methods, especially if several methods can make up for each other's shortcomings. Moreover, the techniques for doing natural and quasi-experimental work, network analysis, and computationally intensive "big data" social science have greatly improved in the last few decades. So today there are six major forms of cross case research. Each has distinctive features--and unique limitations.